Investigators are waiting to interview the driver, who is in hospital under police guard.

People were flying everywhere. We heard ‘thump, thump’. People were running everywhere.A witness, named only as sue, told Melbourne radio station 3AW

Victoria state Premier Daniel Andrews, called the incident an "evil, deliberate, cowardly act" that left 19 people hurt - four of them critically.

In a tweet, police appealed to members of the public to upload any images they might have of the incident to help assist with their investigation.

A witness, named only as Sue, told Melbourne radio station 3AW: "We could hear this noise, as we looked left, we saw this white car, it just mowed everybody down. People were flying everywhere. We heard 'thump, thump'. People were running everywhere."

Another witness, known only as John, told ABC Radio Melbourne that he saw an "SUV coming at high speed".

HEARD

"I really just heard the collision with people with bags and what must be shopping trolleys - and I hope not prams," he said.

"I have really never seen anything like this before, and I have not stopped shaking."

The intersection is one of Melbourne's busiest, a local shop owner told national broadcaster ABC, and is particularly crowded at this time of the year ahead of the Christmas break, with school holidays under way.

This incident comes after a car mowed down pedestrians in Melbourne's busiest mall in January, killing six people.

The driver, whose case is still being heard in court, had been pursued by police prior to the rampage after he had allegedly stabbed his brother.

Canberra has become more worried about home-grown extremism, and officials said they have prevented 13 terror attacks on home soil in recent years.

The Australian government in August unveiled a strategy aimed at preventing vehicle attacks in crowded public places.

Suggested steps include deterrent options such as fencing and closed-circuit cameras, and delaying approaches such as erecting trees and bollards to slow down vehicles.

Melbourne has also been installing a public siren system and more security cameras to warn people of a possible terrorist attack or other serious threats.

Mr Andrews said there would an inquiry into the incident, and whether or not any further changes to Melbourne's security measures needed to be made.

Over the next few days, hundreds more police would patrol the city, he added. - AFP